DESCRIPTION: Intermediate filaments are cell-type specific, and desmin is the intermediate filament found in muscle. This investigator, who has studied desmin since she discovered and characterized the desmin gene as a postdoctoral fellow with Lazarides, has prepared a mouse knockout for desmin. Defects in muscle architecture are observed, and the mice are viable, permitting further analysis, which is now proposed. The application includes three Aims; all designed to test the major current hypotheses for the function of desmin intermediate filaments in muscle. The aims include morphologic and physiologic studies of the knockout mice. Aim 1 is to study how the muscle defects in the desmin knockout mice arise, by examining mice through prenatal development. Skeletal, cardiac and smooth muscle will be examined. Morphology of the myofibrillar apparatus and expression of muscle-specific genes will be examined. Aim 2 is to examine the morphology of the abnormal muscle, using electron microscopy. Both muscle from animals and cultured cell systems will be utilized. The questions are how the fine structure of the myofibril and its interaction with membranes and mitochondria are disturbed by the lack of desmin. Aim 3 is to study the functional properties of the muscle in the desmin knockout mouse, examining standard physiological parameters associated with skeletal, smooth and cardiac muscle. In addition, the ability of the muscle to repair following injury will be examined.